A COMPUTERIZED VENTILATION SYSTEM

Abstract: This invention concerns ventilation systems, and in particular fume cupboards for chemical laboratories and the like. A fan running at constant speed extracts air from the fume cupboard through exhaust ducting, and an auxiliary duct allows air into the exhaust duct. Dampers in the ducts respond to measurements of the movement of the sash at the front of the fume cupboard to control the ratio of air drawn from the cupboard and through the auxiliary duct. The measurements are taken of direction and distance of sash movement, and are re-calibrated to a set point every time the sash passes a predetermined point.

Description: "A COMPUTERIZED VENTILATION SYSTEM" TECHNICAL FIELD The present invention relates to ventilation systems. The invention has been developed primarily for use with fume cupboards for chemical laboratories and the like, and will be described with reference to that application. However, it will be appreciated that the invention is not limited to that particular field of use, and is also applicable to other enclosed spaces, such as rooms, which receive conditioned air for maintaining predetermined conditions. BACKGROUND OF THE INVENTION Fume cupboards provide partially enclosed workplaces, for minimising the dispersion of fumes. The cupboards protect operators and other personnel, and prevent pollution of the local room air. This is generally achieved by extracting the fumes through associated exhaust ducting. Fume cupboards also include selectively movable sashes for providing access to the partially enclosed workplaces. Strict and detailed specifications are set by the Standards Associations of most countries with respect to the minimum safe capture velocity, or air flow velocity, into the partially enclosed workplaces. These standards ensure adequate removal of the fumes. Fume cupboards have utilised a bypass associated with the sash sliding door, and above the sash opening, to supply air from the laboratory into the fume cupboards, and via the exhaust duct towards the exhaust fans, to maintain face and exhaust velocities specified by Standards Associations and State Health Authorities. The sliding sash operates as double valve member, when it starts to rise it starts to close the bypass, and vice versa. For safety reasons a part of the sash will always be uncovered by the sash when in its lowest position allowing some air to pass, but when the sash is fully open the bypass will be totally closed. The air passes through the sash opening and the bypass to dilute the fumes in the fume cupboard always by the same amount. The diluting air is taken out of the laboratory, and if it is conditioned this is a costly waste. Another version has channelled outside air through auxiliary ducts to the bypass to reduce the amount of laboratory air required for efficient dilution of fumes. Methods which supply air through more than one opening into the fume cupboards caused turbulence, and drag fumes from the fume cupboards into the laboratory, endangering the operators and other personnel. An alternative does not use an auxiliary opening, but uses one or more switches operated by the moving sash to control two-speed or multiple-speed fans to maintain safe face velocities. However, these system do not maintain the required high exhaust velocity, and produced unwanted variations in the dilution of the exhausted fumes. The same unsatisfactory effects are achieved using a multiple turn potentiometer associated with the moving sash to control a variable speed fan. Closing the sash results in a restriction in the amount of air leaving the exhaust duct, thereby increasing the concentration level of fumes in the exhaust stack before it extracts to atmosphere with very low exhaust velocity. In addition, these versions have proved to be cumbersome and prone to wear. Additionally, should the sash of such a fume cupboard be left in the fully open position, due to operator error or otherwise, little or no external air is admitted, and the exhaust system extracts only air from the surrounding room. This results in an unnecessary expenditure of energy, both by the extraction system and any air temperature control system used in the laboratory. SUMMARY OF THE INVENTION According to the invention there is provided a fume cupboard, including: a housing defining both a work compartment and an opening to provide access to the compartment; an exhaust duct extending from the compartment; an extraction fan co-operable with the exhaust duct to extract air from the compartment; a movable sash in the opening, operable to close and open at least part of the opening; at least one auxiliary duct communicating with the exhaust duct to provide the exhaust duct with external air; and a measuring means to measure the direction and distance moved by the sash relative to a known position, and to provide a first output signal indicative of the position of the sash; a calibrating means to reset the first output signal to a predetermined value in response to the sash being located at the known position; and at least one moveable damper in the ducts, preferably in the auxiliary duct, responsive to the first output signal to selectively control the rate of flow air through the fume cupboard, and of external air through the auxiliary duct and into the exhaust duct. The system has the advantage of providing precise information concerning the position and the direction of travel of the sash to the control means. Because the calibration means is used to reset the measuring means every time the sash passes a certain point of its travel, the output of the measuring means is not prone to drift, and accuracy is maintained over long periods of use. Because the system has the fan running at a constant number of revolutions per minute, it also enjoys the advantage that the degree of dilution and as a result the concentration of the fumes is maintained constant no matter what the sash position. Optionally the cupboard further comprises at least one mass air flow sensor for providing a second output signal indicative of the mass air flow in the compartment, the damper means being responsive to both the first and second output signals to selectively control the rate of flow of air through the fume cupboard, and of external air through the auxiliary duct into the exhaust duct. This additional feature provides the additional advantage of allowing the controls to take account of ambient conditions, either inside or outside the fume cupboard. Optionally, the measuring means includes a rotary encoder connected to a wheel turned by a cord connected to the sash, or it may be turned by a steel cable joining the sash to a counterweight. Alternatively, the measuring means includes a bar code along either the side of the sash or the side of the opening, and a bar code reader on the other of the side of the sash of the side of the opening. Optionally, the calibrating means is a switch activated by contact, and mounted respectively on one or other of the housing or sash. Optionally, the fume cupboard further comprises a stepper motor responsive to the first, or both, control signals to move the damper. Optionally, the fume cupboard includes a control unit for receiving one at least one output signal and controlling movement of the damper. Optionally, the fume cupboard further includes at least one means for displaying a reading indicative of the position of at least one damper. Optionally, the fume cupboard includes a sensor to provide a signal indicative of activity within the fume cupboard. The sensor may be an infrared transmitter and receiver, proximity sensors or radar sensors, mounted within the fume cupboard. Optionally, the sensor may reset a timer. Optionally, the sash automatically closes by a drive motor if the time has not been reset within a predetermined period of time. In a further aspect the present invention provides a ventilation system for a chamber having at least one opening provided with a selectively operable closing means, ducting connected to supply or remove air from the chamber, fan means co-operable with the ducting to effect the removal or supply; a measuring means to measure the direction and distance moved by the closing means, and to provide a first output signal indicative of the position of the closing means; a calibrating means to reset the first output signal to a predetermined value in response to the closing means being located at a known position; and at least one damper responsive to the first output signal to control the removal or supply of air and maintain a substantially constant predetermined rate of flow of air through the chamber. Optionally, the ventilation system further comprises at least one mass air flow sensor for providing a second output signal indicative of the mass air flow in the chamber. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example only, with reference to the accompanying drawings in which: figure 1 is a front elevation of the housing of a fume cupboard embodying the invention; figure 2 is a partially cut-away elevation of the exhaust duct extending from the fume cupboard of figure 1 ; figure 3 is a partially cut-away side elevation of the exhaust duct showing an alternative embodiment of the damper means; figure 4 is a schematic of a fume cupboard ventilation system embodying the invention; and figure 5 is a cross-section of a fume cupboard embodying the invention. BEST MODE FOR CARRYING OUT THE INVENTION Fume cupboard 1 includes a housing 2 which defines both a work compartment 3 and opening 4 for providing access to the compartment. An exhaust duct 5 extends from compartment 3 and a centrifugal fan 6, driven by an electric motor 7, is co-operable with the exhaust duct for extracting air from the compartment 3 and expelling it through outlet 8. The motor 7 is connected to a constant voltage supply for providing a substantially constant speed of rotation of fan 6. An auxiliary air duct 14 communicates with the exhaust duct 5 between the compartment 3 and the extraction fan 6 for providing the exhaust duct ith external air. The source of external air is usually distinct both from the laboratory air and that expelled through outlet 8. A damper includes two plates 15 and 16 rotatably mounted in the exhaust duct 5 between the fume cupboard and the auxiliary passage, and in the auxiliary passage respectively. Plates 15 and 16 are respectively driven by electric motors 17 and 18. Motors 17 and 18 are stepping motors with 1.8 degree steps and are operated in half stepping mode by a stepper motor driver control 12 via suitable electrical conductors (not shown). Plates 15 and 16 move in opposite senses to maintain a substantially constant cross-sectional area of ducting to supply air to the extraction fan which runs at constant speed. Conditions of the fume cupboard and positions of the sash are able to be measured, and a suitable display 31 is employed to provide information about the cupboard in operation to the operators. Information may also be relayed to a central computer system for further control. For example "power on" indicators for the various components of the cupboard, and various alarm indicators for alerting the operators and management of any potentially dangerous situations, may be provided. The fume cupboard includes a movable sash 11 which may be raised and lowered in the opening 4. The sash includes a sheet of transparent material through which the contents of the compartment 3 can be perceived when the sash is down. The sash is suspended from above by steel cables connected to a counterweight 27. The sash is also connected to counterweight 27 by a cord 28 which travels up and down the rear of the cupboard as the sash is raised and lowered, to drive plastics rollers 33 and 34. A rotary pulse encoder 13 is driven by the cord 28 running over the roller 33. Alternatively the cord may be wrapped around an additional roller if required. This rotary pulse encoder 13 may be of electronic or electromechanical type and has at least two channels with different phases and timing to each other, each providing a convenient number of pulses per revolution. When the sash is propelled from a fully closed to a fully open position, an increased volume of air will be required to be moved through the compartment 3 for the inflow air velocity to be maintained. The encoder 13 will initially signal a movement of the sash, its direction (upward or downward) and the exact length travelled. This information will allow the on-board computer 12 to process the exact required position of the dampers to hold the required air velocities. The computer 12 actuates motor 18 to rotate plate 16 to restrict the passage of external air through the auxiliary duct 14. Simultaneously the computer actuates motor 17 which ill rotate plate 15 in an opposite sense for providing less restriction to the air flow in exhaust duct 5, resulting in an increase in volume of air moving through compartment 3. When the sash moves from an open to a closed position the plates will respond by moving in the opposite directions. There is at least one switch 40 installed to signal a home position of the sash when it is actuated. The home position can be at any predetermined point of the movement of the sash and the computer 12 measures the position of the sash in dependence on the signals received from the rotary encoder, relative to the home position. Air mass flow sensors 9 and 10 detect conditions of the air mass flow, or pressure, resultant from changes in conditions in the surrounding laboratory containing the fume cupboard. Signals from the air mass flow sensors are sent to the on-board computer 12, and these are taken into account with the signals of primary importance received from the encoder 13 and switch 40 to actuate appropriate changes in the positions of the plates 15 and 16. For example wind gusts incident upon damper plates 15 or 16 are continuously accommodated by the control system, thereby preventing any fumes from being redirected back into the fume cupboard through the exhaust duct. Under predetermined conditions the computer 12 will close down the fume cupboard operation by fully closing the dampers. Other ambient conditions, such as a substantial obstruction near the opening, for example a person, will be detected by the air mass flow sensors 9 and 10, and appropriate adjustments to the air flow in the respective ducts will be determined by computer 12. This prevents the occurrence of excessively high air velocity at the opening 4 due to a large volume of air having to be passed through a restricted area. Should the extraction fan 6 no longer perform its desired operation due to a failure or blockage in the ducting system, air mass flow sensors 9 and 10 will correspondingly signal a failure in the maintenance of the predetermined airflow in compartment 3. A suitable alarm is then actuated for signalling such a fault to the operators. The sash 11 can be propelled by a tubular motor 20 such as model 534B produced by Somfy. Following actuation of a manual switch 21 the motor 20, by winching suitable chords 29 and 30, will effect the movement of sash 11. It will be appreciated that a plurality of such switches can be conveniently located for actuating sash movement, such as a foot operable switch (not shown) being located at the base of the fume cupboard or a knee operable switch (not shown) located at the lower edge of the housing. Furthermore, a remote control switch (not shown) utilising infra-red, or other, radiation is able to actuate sash movement. The motor 20 is able to position the sash 11 in any location between a fully open position (as shown in Figure 1 ) and a fully closed position. The motor propels the sash either in a continuous motion or in discrete steps. An infra-red transmitter 23 and receiver 24 are respectively located on opposing sides of the opening 4 to establish an infra-red field across the opening. The output of the sensor 24 is linked to control unit 12 via suitable conductors for allowing the detection of an interruption of the field by an operator or the like. In the event of such an interruption, the control unit resets an associated w . Should the timer be allowed to progress to a predetermined value the control unit actuates motor 20 to effect the closing of sash 11. This feature caters for operator error resulting in the sash being left open, and prevents the unnecessary evacuation of heated or cooled air from the Referring to Figure 3, an alternative damping arrangement is laboratory. Due to the large volume of air which can be removed, this represents the saving of substantial amounts of energy, shown, comprising a single plate 25 located at the junction of the auxiliary air duct 14 and the exhaust duct 5. This arrangement provides for a similar effect as that shown in Figure 2 while only requiring the use of the single plate 25. The plate is hingedly mounted for rotation between fully restricting air flow from the auxiliary duct to a position where it fully restricts air flow from the fume cupboard into exhaust duct 5. The plate is driven by electric motor 26, which in turn is actuated by the control unit 12. The control unit is able to supply all the information it collects to an external source via a connector 35, and can further respond to instructions received from such a source. This facilitates the central control of a plurality of such fume cupboards for example in a large laboratory. Safety conditions are able to be monitored from a central location for providing suitable warning to all operators. In this embodiment connector 35 is a DIN96 or RS-232 serial connector or any other suitable connection to suit the application. Although the invention has been described with reference to specific examples, it should be appreciated that it may be embodied in many other forms. For example there may not be the need to install the damper motor 17 and the damper 15 in certain installations since the motor 18 and the damper 16 can adjust the predetermined mass airflow on their own. In some installations it is preferable that the motor 17 is replaced just by a manual damper adjustment block 19 to bring the damper 15 in a locked position at the time of commissioning. If the fan 6 is correctly matched to the size of the fume cupboard and its associated exhaust system, damper 15 and manual damper adjustment block 19 can be left out altogether. The air flow sensing system may react to mass airflow differences at the sash opening 4 and at the opening of auxiliary duct 14 very rapidly. It may also react to atmospheric pressure changes. The mass airflow and pressure differences are sensed directly in the fume cupboard by the mass air flow sensors 9 and 10 in the fume cupboard. In most installations only one sensor is required for measurements in the fume cupboard and none in any adjoining duct or in front or outside the fume cupboard. On some duct runs the mass air flow sensor might be required to be installed next to the by-pass damper outside the fume cupboard to achieve the highest operator safety. At least one micro switch, or magnetic switch or optical switch or bar code may be mounted or applied to the sash to signal to the electronic control at least one predetermined position of the sash. A number of bar codes between may be applied to the sliding length of the sash or an extension of the sash, and may be read by a reading device to provide the exact position of the sash. The bar codes may alternatively be applied in association with any parts which move in dependence on the sash. Using bar code marks permanent protected against pollutants for sash positioning could replace the rotary encoders. However rotary encoders through their well known reliability are the preferred option. The rotary pulse encoder may be directly driven by the cord running between the sash and the counterbalance and a counterweight, in practice its rotary input arm may form the shaft of one of the pulleys over which that cord runs. Alternatively, the rotary encoder may be geared up or down from one of those pulleys. The output from the rotary encoder is usually in digital form, but may be translated into analog form if required. In another aspect the invention may be applied to a ventilation system for a room including doors and other openings, where associated ducting directs the supply of conditioned air to the room. Rotary encoders and/or bar code marks and air mass flow sensors appropriately positioned are able to supply a signal indicative of the air mass supply to a damper system within the ducting for maintaining a substantially constant predetermined air mass supply in the room or air extraction out of the room.

Claims: THE CLAIMS: 1. A fume cupboard, including: a housing defining both a work compartment and an opening to provide access to the compartment; an exhaust duct extending from the compartment; an extraction fan co-operable with the exhaust duct to extract air from the compartment; a movable sash in the opening, operable to close and open at least part of the opening; at least one auxiliary duct communicating with the exhaust duct to provide the exhaust duct with external air; a measuring means to measure the direction and distance moved by the sash relative to a known position, and to provide a first output signal indicative of the position of the sash; a calibrating means to reset the first output signal to a predetermined value in response to the sash being located at the known position; and at least one moveable damper in the ducts responsive to the first output signal to selectively control the rate of flow of air through the fume cupboard, via the sash opening, and the rate of flow of external air through the auxiliary duct and into the exhaust duct. 2. A fume cupboard according to claim 1 , further comprising at least one mass air flow sensor for providing a second output signal indicative of the mass air flow in the compartment, and the damper means being responsive to both the first and second output signals to selectively control the rate of flow of air through the fume cupboard, and the rate of flow of external air through the auxiliary duct into the exhaust duct. 3. A fume cupboard according to claim 1 or 2, wherein the measuring means includes a rotary encoder connected to a wheel turned by a cord connected to the sash. 4. A fume cupboard according to any preceding claim, wherein the measuring means includes a bar code along either the side of the sash or the side of the opening, and a bar code reader on the other of the side of the sash of the side of the opening. 5. A fume cupboard according to any one of the preceding claims, wherein the calibrating means is a switch activated by contact, and mounted respectively on one or other of the housing or sash. 6. A fume cupboard according to any preceding claim, further comprising a stepper motor responsive to the first, or both, control signals to move the damper. 7. A fume cupboard according to any preceding claim, including a control unit for receiving one or more output signal and controlling movement of the damper. 8. A fume cupboard according to any one of the preceding claims, further including a display for displaying a reading indicative of the position of at least one damper. 9. A fume cupboard according to any preceding claim, further comprising a sensor to provide a signal indicative of activity within the fume cupboard. 10. A fume cupboard according to claim 9, wherein the sensor is an infrared transmitter and receiver, proximity sensors or radar sensors, mounted within the fume cupboard. 11. A fume cupboard according to claims 9 or 10, wherein the signals produced by the sensor are used to reset a timer. 12. A fume cupboard according to claim 11 , wherein the sash automatically closes by a drive motor if the time has not been reset within a predetermined period of time. 13. A fume cupboard according to any preceding claim, wherein the sash is raised and lowered by a motor. 14. A fume cupboard substantially as herein described with reference to the accompanying drawings. 15. A ventilation system for a chamber having at least one opening provided with a selectively operable closing means, ducting connected to supply or remove air from the chamber, fan means co-operable ith the ducting to effect the removal or supply; a measuring means to measure the direction and distance moved by the closing means, and to provide a first output signal indicative of the position of the closing means; calibrating means to reset the first output signal to a predetermined value in response to the closing means being located at a known position; and at least one damper responsive to the first output signal to control the removal or supply of air and maintain a substantially constant predetermined rate of flow of air through the chamber. 16. A ventilation system according to claim 15, further comprising at least one mass air flow sensor for providing a second output signal indicative of the mass air flow in the chamber.

Inventors: STASCH KARL-HEINZ, STASCH, KARL-HEINZ
Applicants: STASCH KARL HEINZ, STASCH, KARL-HEINZ
Application year: 1994
Main classification: B08B15
IPC codes: B08B15